Bacteria such as Streptococci use very fine hairlike structures to cling on to cells and cause infection.

HaeJoo Kang, a PhD student at The University of Auckland, has shown that these hairlike structures, called pili, are made up of hundreds of protein molecules joined end to end, like beads on a string. Even though they are extremely thin, only one molecule wide, these pili are amazingly tough.

With support from Professor Ted Baker and Dr Thomas Proft, HaeJoo discovered that this strength comes from a previously undiscovered cross-link known as an “isopeptide bond”.

She showed this special type of molecular glue not only joined each molecule to the next along the string, but also used the same bonds internally to make itself super-tough. The extra bonding means that the pili can withstand most chemical and mechanical onslaughts.

Other researchers had missed the existence of these bonds before HaeJoo began studying them. Professor Baker says that this work could have potential to make stronger protein materials, as well as its importance for human disease.

“Many bacteria use pili to attach to cells, allowing them to gather together and infect,” Professor Baker says.

“By understanding the structure of the pili, how they are assembled and what gives them their strength, we can also look for their weak points. We may be able to disrupt their ability to attach, or find the means to develop vaccines. Then the body can recognise the pili and destroy the bacteria before they have a chance.”

Streptococcus pyogenes is a bacterium that infects the human throat causing common infections such as sore throats and tonsillitis. It can also be the cause of severe illnesses such as rheumatic fever and streptococcal toxic shock syndrome.